Does Not Boot From SD Card

My first thread. I use 2 android tablets , one which has given me a problem of "twitching" sproradically or constantly. I have downloaded a formware KITKAT4.4 onto an SD card, but the Tablet keeps loading the current software, and doesnt seem to boot up from the SD card. Can anyone help please.
Many thanks,
Fred

from Android Forum http://ift.tt/1dFpzSe
via IFTTT